In various methods for desulfurizing industrial gases, for example, the extracted sulfur is finely dispersed in an aqueous suspension and forms a sulfur paste. Elemental sulfur can be obtained from the paste by drying it; however much more energy can be saved, and greater economies practiced, by heating the paste until the sulfur melts, after which the water and sulfur phases are separated in a settling device as a result of their different densities. In order to prevent the water in the paste from evaporating when the sulfur melts (at approximately 113.degree. C.), the melting process must occur at a pressure of 2 to 5 bars in an autoclave. Sulfur-melting autoclaves of this type have been used in the past, but are limited to batch operations, meaning that the individual steps (i.e., pouring in, melting, phase separation and emptying) occur in succession rather than on a continuous basis.
Copending application Ser. No. 817,655, assigned to the Assignee of this invention, is concerned with a pressure vessel for continuously separating sulfur from an aqueous sulfur suspension in a flow-through process. In order to meet practical operating conditions, the operating temperature should be between 120.degree. C. and 150.degree. C. and the pressure should be between 2 and 5 bars. At the upper temperature limit, there is no increase in the viscosity of liquid sulfur, such as occurs at higher temperatures as a result of molecular processes.
The pressure vessel for continuously separating sulfur from an aqueous suspension is divided into an upper part containing a heating and stirring device and a lower part which serves as a settling tank and has a sulfur outlet at its bottom. Intermediate the upper and lower parts is a horizontal, shallow conical partition having apertures or slots therein. Desirably, the upper part and the lower part are surrounded by a steam-heated jacket.
The annular wall of the upper part tapers downwardly in a conical configuration, the partition having apertures or slots therein being disposed at the lower end of the tapered portion. Heating coils are disposed in the top portion; and a heated fluid flows through them. The heating coils are in the form of vertical cylinders, one within the other, and thus divide the top portion of the pressure vessel into annular chambers. The stirring device in the upper portion can be a centrally-disposed, upwardly conveying propeller. The heating coils in the form of vertical cylinders are disposed around the propeller such that when the propeller is in operation, the contents of the pressure vessel circulate around the heating coils. One of the heating coils forms an annular chamber with the outer wall of the upper portion of the pressure vessel. This annular chamber is open at the top and bottom and communicates with an outlet of water separated in the annular chamber.
Devices are provided for measuring the differential pressure between the surface of the water in the upper portion of the pressure vessel and the boundary surface between the water phase and the sulfur phase in the lower part. Regulating devices regulate the withdrawal of water and sulfur in dependence on the pressure at the water surface in the upper portion and the differential pressure at the boundary surface between the water phase and the sulfur phase in the lower portion. Sludge can be removed through conduits placed near the boundary surface between the water phase and the sulfur phase.
During operation, droplets of the molten sulfur collect and sink downwardly because of their greater density while the water rises in the outer annular chamber for discharge from the pressure vessel through a top outlet. The sulfur paste processed in the pressure vessel of this type may also contain very small sulfur particles depending upon the preceding process. The rate of suspension of these particles after melting is below the rate of ascent of the water in the outer annular chamber. The fine sulfur particles are not separated from the water in the vessel in this instance and are discharged from the vessel together with the water through the top outlet.